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Aad, G., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J., . . . et al., . (2020). Combination of searches for Higgs boson pairs in pp collisions at root s=13 TeV with the ATLAS detector. Physics Letters B, 800, Article ID 135103.
Open this publication in new window or tab >>Combination of searches for Higgs boson pairs in pp collisions at root s=13 TeV with the ATLAS detector
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2020 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 800, article id 135103Article in journal (Refereed) Published
Abstract [en]

This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb(-1) of proton-proton collision data at a centre-of-mass energy root s = 13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the b (b) over barb (b) over bar, b (b) over barW(+)W(-), b (b) over bar tau(+)tau(-), W+W-W+W-, b (b) over bar gamma gamma and W+W-gamma gamma final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (kappa(lambda)) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to -5.0 < kappa(lambda) < 12.0 (-5.8 < kappa(lambda) < 12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model.

Place, publisher, year, edition, pages
ELSEVIER, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-266934 (URN)10.1016/j.physletb.2019.135103 (DOI)000503832500009 ()2-s2.0-85075879322 (Scopus ID)
Note

QC 20200130

Available from: 2020-01-30 Created: 2020-01-30 Last updated: 2020-01-30Bibliographically approved
Aaboud, M., Kastanas, K. A., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . et al., . (2020). Combined measurements of Higgs boson production and decay using up to 80 fb(-1) of proton-proton collision data at root S=13 TeV collected with the ATLAS experiment. Physical Review D: covering particles, fields, gravitation, and cosmology, 101(1), Article ID 012002.
Open this publication in new window or tab >>Combined measurements of Higgs boson production and decay using up to 80 fb(-1) of proton-proton collision data at root S=13 TeV collected with the ATLAS experiment
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2020 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 101, no 1, article id 012002Article in journal (Refereed) Published
Abstract [en]

Combined measurements of Higgs boson production cross sections and branching fractions arc presented. The combination is based on the analyses of the Higgs boson decay modes H -> gamma gamma, ZZ*, WW*, tau tau, b (b) over bar, mu mu, searches for decays into invisible final states, and on measurements of off-shell Higgs boson production. Up to 79.8 fb(-1) of proton-proton collision data collected at root S = 13 TeV with the ATLAS detector are used. Results are presented for the gluon-gluon fusion and vector-boson fusion processes, and for associated production with vector bosons or top-quarks. The global signal strength is determined to be mu = 1.11(-0.08)(+0.09). The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of 6.5 sigma (5.3 sigma). Measurements in kinematic regions defined within the simplified template cross section framework are also shown. The results are interpreted in terms of modifiers applied to the Standard Model couplings of the Higgs boson to other particles, and are used to set exclusion limits on parameters in two-Higgs-doublet models and in the simplified minimal supersynunetric Standard Model. No significant deviations from Standard Model predictions are observed.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-266930 (URN)10.1103/PhysRevD.101.012002 (DOI)000505485600001 ()
Note

QC 20200131

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-01-31Bibliographically approved
Aad, G., Jensen, B., Ohm, C., Ripellino, G., Strandberg, J. & Zwalinski, L. (2020). Measurement of differential cross sections for single diffractive dissociation in root s=8 TeV pp collisions using the ATLAS ALFA spectrometer. Journal of High Energy Physics (JHEP) (2), Article ID 42.
Open this publication in new window or tab >>Measurement of differential cross sections for single diffractive dissociation in root s=8 TeV pp collisions using the ATLAS ALFA spectrometer
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2020 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 2, article id 42Article in journal (Refereed) Published
Abstract [en]

A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy s= 8 TeV is used to study inclusive single diffractive dissociation, pp -> X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is -4.0 < log(10)xi < -1.6 and 0.016 < |t| < 0.43 GeV2, where xi is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 +/- 0.13 mb. Cross sections are also measured differentially as functions of xi, t, and increment eta, a variable that characterises the rapidity gap separating the proton and the system X . The data are consistent with an exponential t dependence, d sigma/dt proportional to e(Bt) with slope parameter B = 7.65 +/- 0.34 GeV-2. Interpreted in the framework of triple Regge phenomenology, the xi dependence leads to a pomeron intercept of alpha(0) = 1.07 +/- 0.09.

Place, publisher, year, edition, pages
SPRINGER, 2020
Keywords
Diffraction, Forward physics, Hadron-Hadron scattering (experiments), QCD
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-270919 (URN)10.1007/JHEP02(2020)042 (DOI)000515812400002 ()2-s2.0-85079500025 (Scopus ID)
Note

QC 20200316

Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
Aaboud, M., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J., . . . et al., . (2020). Measurement of J/psi production in association with a W-+/- boson with pp data at 8 TeV. Journal of High Energy Physics (JHEP) (1), Article ID 95.
Open this publication in new window or tab >>Measurement of J/psi production in association with a W-+/- boson with pp data at 8 TeV
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2020 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, article id 95Article in journal (Refereed) Published
Abstract [en]

A measurement of the production of a prompt J/psi meson in association with a W-+/- boson with W-+/- -> mu nu and J/psi -> mu(+)mu(-) is presented for J/psi transverse momenta in the range 8.5-150 GeV and rapidity |y(J/psi)| < 2.1 using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton-proton centre-of-mass energy of s = 8 TeV and correspond to an integrated luminosity of 20.3 fb(-1). The ratio of the prompt J/psi plus W-+/- cross-section to the inclusive W-+/- cross-section is presented as a differential measurement as a function of J/psi transverse momenta and compared with theoretical predictions using different double-parton-scattering cross-sections.

Place, publisher, year, edition, pages
SPRINGER, 2020
Keywords
Hadron-Hadron scattering (experiments)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-269490 (URN)10.1007/JHEP01(2020)095 (DOI)000511676700001 ()2-s2.0-85078165339 (Scopus ID)
Note

QC 20200309

Available from: 2020-03-09 Created: 2020-03-09 Last updated: 2020-03-09Bibliographically approved
Aad, G., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J., . . . et al., . (2020). Measurement of the azimuthal anisotropy of charged-particle production in Xe plus Xe collisions at root S-NN=5.44 TeV with the ATLAS detector. Physical Review C: Covering Nuclear Physics, 101(2), Article ID 024906.
Open this publication in new window or tab >>Measurement of the azimuthal anisotropy of charged-particle production in Xe plus Xe collisions at root S-NN=5.44 TeV with the ATLAS detector
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2020 (English)In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 101, no 2, article id 024906Article in journal (Refereed) Published
Abstract [en]

This paper describes the measurements of flow harmonics v(2)-v(6) in 3 mu b(-1) of Xe Xe collisions at root S-NN = 5.44 TeV performed using the ATLAS detector at the Large Hadron Collider (LHC). Measurements of the centrality, multiplicity, and p(T) dependence of the v(n) obtained using two-particle correlations and the scalar product technique are presented. The measurements are also performed using a template-fit procedure, which was developed to remove nonflow correlations in small collision systems. This nonflow removal is shown to have a significant influence on the measured v(n) at high p(T), especially in peripheral events. Comparisons of the measured v(n) with measurements in Pb + Pb collisions and p + Pb collisions at root S-NN = 5.02 TeV are also presented. The v(n) values in Xe + Xe collisions are observed to be larger than those in Pb + Pb collisions for n = 2, 3, and 4 in the most central events. However, with decreasing centrality or increasing harmonic order n, the v(n) values in Xe + Xe collisions become smaller than those in Pb + Pb collisions. The v(n) in Xe + Xe and Pb + Pb collisions are also compared as a function of the mean number of participating nucleons, < N-part >, and the measured charged-particle multiplicity in the detector. The v(3) values in Xe + Xe and Pb + Pb collisions are observed to be similar at the same < N-part > or multiplicity, but the other harmonics are significantly different. The ratios of the measured v(n) in Xe + Xe and Pb + Pb collisions, as a function of centrality, are also compared to theoretical calculations.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-269462 (URN)10.1103/PhysRevC.101.024906 (DOI)000513213800003 ()
Note

QC 20200310

Available from: 2020-03-10 Created: 2020-03-10 Last updated: 2020-03-10Bibliographically approved
Aad, G., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J., . . . et al., . (2020). Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb(-1) of pp collisions at root s=13 TeV with the ATLAS experiment. Physics Letters B, 800, Article ID 135082.
Open this publication in new window or tab >>Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb(-1) of pp collisions at root s=13 TeV with the ATLAS experiment
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2020 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 800, article id 135082Article in journal (Refereed) Published
Abstract [en]

A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb(-1) of proton-proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a b-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the tq gamma coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC t gamma production via a left-handed (right-handed) tu gamma coupling of 36 fb (78 fb) and on the branching ratio for t -> gamma u of 2.8 x 10(-5) (6.1 x 10(-5)). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC t gamma production via a left-handed (right-handed) tc.coupling of 40 fb (33 fb) and on the branching ratio for t -> gamma c of 22 x 10(-5) (18 x 10(-5)).

Place, publisher, year, edition, pages
ELSEVIER, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-266933 (URN)10.1016/j.physletb.2019.135082 (DOI)000503832500051 ()2-s2.0-85075235650 (Scopus ID)
Note

QC 20200130

Available from: 2020-01-30 Created: 2020-01-30 Last updated: 2020-01-30Bibliographically approved
Aad, G., Lund-Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J. & Zwalinski, L. (2020). Search for Magnetic Monopoles and Stable High-Electric-Charge Objects in 13 Tev Proton-Proton Collisions with the ATLAS Detector. Physical Review Letters, 124(3), Article ID 031802.
Open this publication in new window or tab >>Search for Magnetic Monopoles and Stable High-Electric-Charge Objects in 13 Tev Proton-Proton Collisions with the ATLAS Detector
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2020 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, no 3, article id 031802Article in journal (Refereed) Published
Abstract [en]

A search for magnetic monopoles and high-electric-charge objects is presented using 34.4 fb(-1) of 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015 and 2016. The considered signature is based upon high ionization in the transition radiation tracker of the inner detector associated with a pencil-shape energy deposit in the electromagnetic calorimeter. The data were collected by a dedicated trigger based on the tracker high-threshold hit capability. The results are interpreted in models of Drell-Yan pair production of stable particles with two spin hypotheses (0 and 1/2) and masses ranging from 200 to 4000 GeV. The search improves by approximately a factor of 5 the constraints on the direct production of magnetic monopoles carrying one or two Dirac magnetic charges and stable objects with electric charge in the range 20 <= vertical bar z vertical bar <= 60 and extends the charge range to 60 < vertical bar z vertical bar <= 100.

Place, publisher, year, edition, pages
American Physical Society, 2020
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-268812 (URN)10.1103/PhysRevLett.124.031802 (DOI)000509506300003 ()32031842 (PubMedID)2-s2.0-85079081039 (Scopus ID)
Note

QC 20200224

Available from: 2020-02-24 Created: 2020-02-24 Last updated: 2020-02-24Bibliographically approved
Aad, G., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J., . . . et al., . (2020). Searches for lepton-flavour-violating decays of the Higgs boson in root s=13 TeV pp collisions with the ATLAS detector. Physics Letters B, 800, Article ID 135069.
Open this publication in new window or tab >>Searches for lepton-flavour-violating decays of the Higgs boson in root s=13 TeV pp collisions with the ATLAS detector
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2020 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 800, article id 135069Article in journal (Refereed) Published
Abstract [en]

This Letter presents direct searches for lepton flavour violation in Higgs boson decays, H -> e tau and H -> mu tau, performed with the ATLAS detector at the LHC. The searches are based on a data sample of proton-proton collisions at a centre-of-mass energy root s = 13 TeV, corresponding to an integrated luminosity of 36.1 fb(-1). No significant excess is observed above the expected background from Standard Model processes. The observed (median expected) 95% confidence-level upper limits on the lepton-flavour-violating branching ratios are 0.47%(0.34(-0.10)(+0.13)%) and 0.28%(0.37(-0.10)(+0.14)%) for H -> e tau and H -> mu tau, respectively.

Place, publisher, year, edition, pages
ELSEVIER, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-266932 (URN)10.1016/j.physletb.2019.135069 (DOI)000503832500048 ()2-s2.0-85074945898 (Scopus ID)
Note

QC 20200131

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-01-31Bibliographically approved
Aaboud, M., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., Strandberg, J. & Zwalinski, L. (2020). Transverse momentum and process dependent azimuthal anisotropies in root S-NN=8.16 TeV p plus Pb collisions with the ATLAS detector. European Physical Journal C, 80(1), Article ID 73.
Open this publication in new window or tab >>Transverse momentum and process dependent azimuthal anisotropies in root S-NN=8.16 TeV p plus Pb collisions with the ATLAS detector
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2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, no 1, article id 73Article in journal (Refereed) Published
Abstract [en]

The azimuthal anisotropy of charged particles produced in sNN=8.16TeV p+Pb collisions is measured with the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 165 nb-1 that was collected in 2016. Azimuthal anisotropy coefficients, elliptic v2 and triangular v3\, extracted using two-particle correlations with a non-flow template fit procedure, are presented as a function of particle transverse momentum (pT) between 0.5 and 50 GeV. The v2 results are also reported as a function of centrality in three different particle pTintervals. The results are reported from minimum-bias events and jet-triggered events, where two jet pT thresholds are used. The anisotropies for particles with pT less than about 2 GeV are consistent with hydrodynamic flow expectations, while the significant non-zero anisotropies for pT in the range 9-50 GeV are not explained within current theoretical frameworks. In the pTrange 2-9 GeV, the anisotropies are larger in minimum-bias than in jet-triggered events. Possible origins of these effects, such as the changing admixture of particles from hard scattering and the underlying event, are discussed.

Place, publisher, year, edition, pages
SPRINGER, 2020
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-270918 (URN)10.1140/epjc/s10052-020-7624-4 (DOI)000513720900001 ()2-s2.0-85079172889 (Scopus ID)
Note

QC 20200316

Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
Aaboud, M., Kastanas, K. A., Jensen, B., Ohm, C., Ripellino, G., Sidebo, P. E., . . . Zwalinski, L. (2019). A strategy for a general search for new phenomena using data-derived signal regions and its application within the ATLAS experiment. European Physical Journal C, 79(2), Article ID 120.
Open this publication in new window or tab >>A strategy for a general search for new phenomena using data-derived signal regions and its application within the ATLAS experiment
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2019 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 79, no 2, article id 120Article in journal (Refereed) Published
Abstract [en]

This paper describes a strategy for a general search used by the ATLAS Collaboration to find potential indications of new physics. Events are classified according to their final state into many event classes. For each event class an automated search algorithm tests whether the data are compatible with the Monte Carlo simulated expectation in several distributions sensitive to the effects of new physics. The significance of a deviation is quantified using pseudo-experiments. A data selection with a significant deviation defines a signal region for a dedicated follow-up analysis with an improved background expectation. The analysis of the data-derived signal regions on a new dataset allows a statistical interpretation without the large look-elsewhere effect. The sensitivity of the approach is discussed using Standard Model processes and benchmark signals of new physics. As an example, results are shown for 3.2fb-1 of proton-proton collision data at a centre-of-mass energy of 13TeV collected with the ATLAS detector at the LHC in 2015, in which more than 700 event classes and more than 105 regions have been analysed. No significant deviations are found and consequently no data-derived signal regions for a follow-up analysis have been defined.

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-244519 (URN)10.1140/epjc/s10052-019-6540-y (DOI)000457998500007 ()2-s2.0-85061187220 (Scopus ID)
Note

QC 20190403

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-04-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-5935-7464

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